Autoimmune diseases are a family of related illnesses which possess a common characteristic feature, the immune system, originally intended to provide protection from the invasion of foreign pathogens, turns upon itself, attacking self tissues and organs. The purpose of this Phase I proposal is to isolate and characterize the target kidney cell autoantigen found to bind a therapeutic monoclonal antibody 3El0, which has been shown to be effective in turning off production of destructive antoantibodies in systemic lupus nephritis. Characterization of the antigenic moiety bound by 3El0, and immunoscreening of expression cDNA libraries will be performed. In Phase II, we propose to carry out detailed structure-function studies and use the autoantigen for developing immunotherapy peptide and monoclonal studies.